I have been playing with it and didn't get index() to work, mainly because index always returns the first instance of the string if it occurs multiple times. I assume that normally it would be different values and then it wouldn't matter. But just in case the email is repeated somewhere in your lists, the only way I could get it to work was like this:

for a in range(len(list)):
if '@' in list[a]: print list[a],
else:
if a < (len(list)-1):
if '@' in list[a + 1]:
print list[a]
else:
print list[a],
else:
print list[a]